This article reviews the diagnostic criteria for both myalgic encephalomyelitis (ME) (ie, chronic fatigue syndrome) and fibromyalgia (FM) and describes how to differentiate them from depressive and anxiety disorders, the psychiatric conditions with which they are most often confused. The patients in the following Case Vignettes have ME and/or FM; not all have a psychiatric condition.

Despite thousands of peer-reviewed papers documenting their unique characteristics and pathophysiology, ME and FM continue to be mistaken for psychiatric conditions. This is problematic because it can delay accurate diagnosis and appropriate treatment, often for years. Although they have some symptoms in common (eg, fatigue, cognitive problems, unrefreshing sleep), ME and FM differ from each other and from all known psychiatric conditions. Diagnostic clarity depends on knowledge of the diagnostic criteria for each condition and identifying the pathognomonic, non-overlapping symptoms.

Diagnostic criteria for myalgic encephalomyelitis

The Canadian Consensus Criteria are used for diagnosis of ME. These criteria require the concurrent presence of disabling fatigue, postexertional malaise, unrefreshing sleep, muscle or joint pain, mood or cognitive symptoms, and at least 2 of the following: autonomic, neuroendocrine, or immune symptoms (Table 1).1 Postexertional malaise (immediate or delayed), the pathognomonic symptom of ME, is unusual in any psychiatric condition: most psychiatric patients feel better rather than worse after mental or physical exertion. Pain is not a core symptom of any common psychiatric condition but is reported to be elevated in major depression.2 Autonomic, neuroendocrine, and immune symptoms are not common in any psychiatric condition.

What new information does this article provide?

? Myalgic encephalomyelitis (ME) and fibromyalgia (FM) are complex biomedical conditions. Because psychiatric conditions are commonly comorbid, they should be looked for in patients with ME and FM.

What are the implications for psychiatric practice?

? Consider the diagnoses of ME and FM in “psychiatric” patients with a disproportionate number of physical symptoms, especially in those who are not responding as expected to psychiatric interventions.

Diagnostic criteria for fibromyalgia

New criteria for diagnosing FM were published in 2010.3 These criteria eliminate the previously required need for tender points on physical examination and add the criteria of fatigue, unrefreshing sleep, cognitive symptoms, and a long list of somatic symptoms (none of which are specific to FM) to the pathognomonic symptom of widespread pain (Table 2). Since fatigue, unrefreshing sleep, and cognitive symptoms are common to many psychiatric conditions, these new criteria do not aid in the differentiation between FM and a psychiatric diagnosis. A careful review of the entire constellation of symptoms is needed to identify whether the psychological or physical symptoms predominate. In patients with aching, tiring pain all over as the primary presenting symptom in combination with several other somatic symptoms, FM should be considered.

CASE VIGNETTES

Maggie, aged 51, has suffered from chronic pain for several years since a skiing accident resulted in multiple surgeries on her broken ankle. In the past few years, this pain has become more generalized and is now associated with fatigue and cognitive problems. As she became increasingly unable to work, play, and socialize, depression developed. Now she feels “sick and tired” all the time with “pain all over” and lacks hope for the future.

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Ben, aged 30, was a football star in college before coming down with Epstein Barr virus infection. He did not rest when he became ill because it was right before playoffs. He never fully recovered from this infection. He continues to feel “flu-like” most of the time and his energy “crashes” anytime he tries to do even modest amounts of exercise, such as playing with his young children. Since becoming ill, he has noticed a generalized worry about life. Even though his wife works and he has good family support, he cannot suppress the worry that “it will all fall apart.”

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Joyce, aged 40, developed fatigue, “brain fog,” and “pain all over” after the difficult, premature birth of her second child. The child did not sleep through the night until he was 5 years old. When this child was 6 and starting school, Joyce thought she would finally be able to catch up on her sleep and rest. However, her health unaccountably took a turn for the worse and she experienced increased fatigue, orthostatic dizziness, difficulty in regulating temperature, and severe postexertional malaise. Her family physician diagnosed depression and prescribed an antidepressant. This, and other subsequent psychotropic trials, made her symptoms worse. She says she does not feel depressed, just really ill.

Prevalence of comorbidity

ME and FM can exist alone or together or can be comorbid with psychiatric conditions. The prevalence of Axis I conditions, particularly mood disorders, is higher in patients who have ME and FM than in healthy controls. The prevalence of psychiatric comorbidity is about the same in patients with ME as in patients with other chronic medical conditions; however, the rates are higher in patients who have FM. Estimates of comorbidity vary widely from study to study, which may be due to differences in sample types, variance in assessment tools for psychiatric diagnosis, and varying criteria being used for ME and FM. The variance is great enough that trying to estimate rates for individual comorbid psychiatric conditions is not helpful.

The prevalence of concurrent Axis I conditions among patients with ME ranges from 25% to 57%.4-6 The upper estimate comes from an epidemiological study that used flawed diagnostic criteria for ME.5,7 There is no evidence of any special relationship between ME and any psychiatric condition. In persons with ME, the prevalence of personality disorders is similar to that in the general population (less than10%) and much lower than that found in patients with depression.8,9

Rates of depression and anxiety are also variable in FM. The prevalence of “depressive disorders” ranges from 20% to 80% and of “anxiety disorders,” from 13% to 64%.10 Axis II diagnoses are identified in 8.7% of patients with FM.11 There is some overlap in the genetics and family clustering of FM, MDD, and dysthymia.12,13 In a recently published review on the connection between depression and FM, Gracely and colleagues14 conclude that while some categorize FM as an “affective spectrum disorder,” there are many alternative explanations for the high rates of depression and anxiety in patients with FM. Despite overlapping symptoms and family clustering, current opinion is that FM is not primarily an affective disorder.12,15